GALICIA, SPAIN—A lidar survey of a forested hilltop in northwestern Spain conducted by Mário Fernández-Pereiro of University College London and the University of Santiago de Compostela and José Carols Sánchez-Pardo of the University of Santiago de Compostela has revealed an early medieval fortress, according to a Live Science report. The study suggests that the site, known as Castro Valente, had 30 towers, covered about 25 acres, and was surrounded by a defensive wall. Dated to the fifth century A.D. based on pottery found at the site and construction methods, the structure is thought to have been built on top of an earlier Iron Age fort as protection from invasion after the collapse of Roman rule in the region. The fort is thought to have been abandoned about 200 years later. To read about medieval sculpture in the Cathedral of Santiago de Compostela, go to "Around the World: Spain."